The invention relates to an apparatus and a transmissive display arrangement.
The invention also relates to a control circuit in a transmissive display arrangement. The invention may be used for the display of a video signal on a transmissive non-emitting display system.
The invention further relates to a storage medium for storing instructions for carrying out a method of adjusting a backlight signal in a transmissive display arrangement.
Displays can be divided into self-emitting displays and non-emitting displays. A CRT (Cathode Ray Tube) display is a representative of self-emitting devices. A Liquid Crystal Display (LCD) is a non-emitting device, in which the liquid crystal regulates the light transmittance. Since the LCD itself does not produce light, light must be obtained from an external source. In a reflective system, ambient light is used. A reflective system produces a display by reflecting ambient light from a highly reflective film that is fixed on the far side of the panel. In a transmissive system, a light source is provided at the rear of the LCD panel in order to supply illumination from the back. The light source used in a transmissive system is called a backlight. The prominent type of backlight is small fluorescent tubes mounted with a special mechanism that transforms the line-source light beam emerging from the fluorescent tubes into an area-wide illumination to cover the entire panel. Another emerging type of backlight is Light Emitting Diodes (LED) that have the advantage of permitting fast switching.
U.S. Pat. No. 5,870,154 discloses a circuit and method for optimizing the display of a video signal on a display. Control of the display""s brightness and contrast is based on aspects of the video signal, such as the average amplitude of the signal and the standard deviation. These aspects of the video signal are determined and the video signal is manipulated based on the determined characteristics such that the resultant video signal is optimized to the dynamic range of the display.
In such a known circuit, an identification circuit analyzes a conditioned video signal to identify properties of the video signal, e.g. the minimum and maximum amplitudes of the video signal and based on the identified properties, causes a signal conversion circuit to modify the data provided to the display unit to utilize a greater portion of the display""s dynamic range.
Known methods adjust the video signal without influencing the backlight signal.
It is an object of the invention to take advantage of the robustness and fast switching capability of an LED backlight arrangement of a transmissive display.
It is another object of the invention to provide a transmissive display arrangement that allows lowering the power consumption of backlight means.
It is yet another object of the invention to provide a low-power consumption display arrangement or apparatus.
To this end, an apparatus of the invention comprises:
a transmissive display arrangement;
an arrays of cells;
video controlling means for deriving an adjusted video signal from an initial video signal representing a frame to be displayed by the display arrangement; and,
backlight means for providing a backlight signal to the array in response to a backlight control signal associated with the frame;
backlight controlling means, coupled to the video controlling means, for deriving the backlight control signal from the initial video signal and the adjusted video signal.
Such an apparatus comprises an array of cells and the video signal is applied to at least one of the cells. Besides, the display arrangement comprises the backlight means transmitting the backlight signal to the cell in response to the backlight control signal. Thus, from the video and the backlight signals, the cell may produce a displayed output. The invention comprises determining the video signal to be provided to the cell, hereafter referred to as the adjusted video signal. The invention also comprises determining the backlight control signal to be provided to the backlight means, hereafter referred to as the backlight control signal. The backlight control signal and the adjusted video signal are determined for a given frame to be displayed by the display arrangement. The adjusted video signal may be determined either arbitrarily, from characteristics of the initial video signal such as a distribution property of the initial video signal as explained hereinafter, or from any other parameter of the display arrangement. The backlight control signal is determined from the adjusted video signal and from the initial video signal. In another embodiment, the backlight control signal is also further derived based on an initial control signal. The invention allows modulating and more precisely lowering the backlight signal, through the modulation of the backlight control signal, by modifying the initial video signal. As a result, by enabling lowering the backlight signal, the invention permits power savings. An apparatus of the invention may allow to have such a described process quasi-transparent to a user. Indeed, the backlight control signal may be determined so that the cell would lead to comparable displayed outputs when receiving the initial video signal and an initial backlight signal, corresponding to an initial backlight control signal, as it would when receiving the adjusted backlight signal and the adjusted backlight signal.
Such an apparatus may comprise an LCD arrangement, for which the backlight means comprises an LED arrangement. The fast switching capability of an LED allows adjusting the backlight signal and determining the adjusted video signal for each displayed frame at the refresh rate of the display arrangement.
In another embodiment of the invention, the video controlling means is further configured to determine the adjusted video signal based on a distribution property of the initial video signal.
In such an embodiment, basing the adjustment of the initial video signal on its distribution property permits determining an adjusted video signal that covers the entire value range available for the video signal to be ultimately provided to the cells. As a consequence the backlight control signal may be determined such that it optimizes the generation of the backlight signal.
In yet another embodiment of the invention, the backlight controlling means is configured to further derive the backlight control signal from a maximum allowed value for the initial video signal and from a reference value of the initial video signal. The reference value may be determined from a distribution property of the initial video signal. In this embodiment, the video controlling means is configured to derive, for each cell of the array, a value of the adjusted video signal associated with the cell based on said reference value, said maximum allowed value and a value of the initial video signal associated with the cell.
In this embodiment, the reference value may be determined from a comparison of values of the initial video signal, each value being respectively associated with a cell of the array. The initial video signal may not use values greater than the maximum allowed value. The reference value is therefore lower than this maximum allowed value. The reference value of the initial video signal may then be adjusted to the maximum allowed value of the video signal. In this embodiment, the backlight control signal may then be determined based on the reference value and on the maximum allowed value. In an embodiment, where the reference value is the greatest value of the initial video signal associated with a given frame, the backlight signal may be lowered at a minimum for the frame. An advantage of one or more embodiments of the invention is to allow lowering at a minimum the backlight intensity in a transmissive display thereby enabling efficient power savings.